Rotatable patella drill guide

ABSTRACT

A patella drill guide includes a base portion rotatably mounted on a bone-gripping component. A trial portion with a contoured articulation surface is above the base portion. The base portion and trial portion have aligned drill guide bores. The base portion and trial portion can be rotated together on the bone-gripping component to optimize the positions of the drill guide bores with respect to the patella surface, thereby optimizing the locations of the mounting pegs of the patella implant component on the patella to optimize the orientation of the patella implant component. The base and the bone-gripping component may be unitary so that the entire assembly rotates on the patella about the central longitudinal axis of the bone-gripping component.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Prov. App. No. 61/540,040entitled “Rotatable Patella Drill Guide,” filed Sep. 28, 2011. Thepresent application is also a continuation of U.S. Publication No.20130079787A1 (U.S. patent application Ser. No. 13/548,598) entitled“Rotatable Patella Drill Guide” filed on Jul. 13, 2012, both of whichare incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to orthopaedic surgicalinstruments and more particularly to patella drill guides.

BACKGROUND

During the lifetime of a patient, it may be necessary to perform a jointreplacement procedure on the patient as a result of, for example,disease or trauma. The joint replacement procedure may involve the useof a prosthesis which is implanted into one or more of the patient'sbones. In the case of a patella replacement procedure, an orthopaedicprosthesis is implanted into the patient's patella. Specifically, aprosthetic patella implant component is secured to the patient's naturalpatella such that its posterior surface articulates with a femoralcomponent during extension and flexion of the knee.

To facilitate the replacement of the articulating surface of the naturalpatella with the prosthetic patella, orthopaedic surgeons use a varietyof orthopaedic surgical instruments such as, for example, saws, drills,mills or reamers to resect the posterior surface of the patella and thento prepare the resected surface for fixation of the prosthetic patella.

Common fixation elements for prosthetic patellae include one or morepegs extending out from the bone-facing (anterior) surface to bereceived in complementary recesses or holes drilled or reamed into thepatella.

In some prosthetic patella implants, the articulating surface isdome-shaped, as in U.S. Pat. No. 5,593,450. In other types of prostheticpatella implants, the articulating surface has an asymmetric shape to bereceived and track within the patellar groove in the prosthetic femoralimplant component. An example of such an asymmetrically-shapedprosthetic patella is disclosed in U.S. Pat. No. 6,074,425. With suchasymmetric patella implants, rotational alignment of the implant impactsthe way in which the patella implant tracks in the trochlear groove ofthe femoral implant. Such asymmetric patella implants typically includea plurality of pegs extending out from the anterior surface to bereceived in the complementary holes drilled in the patella surface.However, the surgeon typically cannot fully evaluate patellar trackinguntil trial patellar and femoral components are in place, whichgenerally requires that the complementary holes be drilled before thetrial is placed on the resected patella. If the surgeon determines thatthe patella trial does not track correctly, there is little opportunityto make adjustments since the mounting holes have already been drilledinto the resected patella surface.

SUMMARY

The present invention provides a patella drill guide that allows thesurgeon to evaluate patella tracking before drilling mounting holes intothe resected surface of the patella.

In illustrative embodiments, the present invention provides such apatella drill guide for use in preparing a resected patellar bonesurface to receive a prosthetic patellar implant component. The patelladrill guide comprises a bone-gripping component, a base portion and apatella trial portion. The bone-gripping component is for gripping aportion of the resected patellar bone surface. The base portion has aflat patella bone-facing surface and a portion of the bone-grippingcomponent extends outwardly from the flat patella bone-facing surface ofthe base. The patella trial portion has a contoured articulation surfacespaced above the flat patella bone-facing surface of the base portion.The base portion has a plurality of drill guide bores extending throughthe base portion to the flat patella bone-facing surface of the baseportion.

In a particular embodiment, the base is rotatably mounted on thebone-gripping component. In such an embodiment, the positions of thedrill guide bores with respect to the resected patellar surface changeas the base portion is rotated on the bone-gripping component.

Such a patella drill guide can be temporarily mounted on the resectedposterior surface of the patella and used to evaluate the size and setthe orientation of the patella trial portion prior to drilling holes inthe patella; once the surgeon is satisfied with the orientation of thepatella trial portion, the surgeon may use the patella drill guide todrill properly oriented and positioned holes to receive and properlyorient the patella implant component.

In a more particular embodiment, the bone-gripping component comprises apedestal and a plurality of spikes extending outwardly from a pedestal.In this embodiment, the base is rotatably mounted on the pedestal.

In another more particular embodiment, the patella trial portion has aplurality of bores aligned with the drill guide bores of the base. Thealignment of the drill guide bores and bores of the patella trialportion does not change as the base portion is rotated on thebone-gripping component. In such a device with aligned bores in thepatella trial portion, the portion of each bore through the patellatrial portion may have a larger diameter than the aligned portion ofsuch bore through the base portion.

In another more particular embodiment, the base portion and the patellatrial portion are integral.

In another more particular embodiment, the base portion and the patellatrial portion comprise independent components connected to define anassembly. In this embodiment, the base portion may have an upper orsecond surface spaced from and parallel to the flat patella bone-facingsurface. In such an embodiment, the base portion may have an edge thatextends between the upper surface and the patella bone-facing surface.The edge may include a plurality of spaced recesses and the uppersurface may include indicia adjacent to the spaced recesses. In such anembodiment, the patella trial portion may have a flat surface spacedfrom the contoured articulation surface and the flat surface of thepatella trial portion may be fixed to the second flat surface of thebase. In such an embodiment, the base portion may have a constantthickness or alternatively may have an thicker portion adjacent to thedrill guide bores and thinner portions adjacent to the spaced recesses.

In another more particular embodiment, the base portion includes a firstend portion and a second end portion connected by an arm. In thisembodiment, the first end portion of the base portion is rotatablymounted on the bone-gripping component, the patella trial portion ispart of the first end portion of the base portion and the second endportion of the patella drill guide includes a second bone-grippingcomponent, a second base portion having a flat patella bone-facingsurface, and a second patella trial portion having a contouredarticulating surface. In this embodiment, the second base portion isrotatably mounted on the second bone-gripping component with a portionof the second bone-gripping component extending outwardly from the flatpatella bone-facing surface, the second patella trial portion has acontoured articulation surface spaced above the flat patella bone-facingsurface of the second base portion and the second base portion and thesecond patella trial portion have a plurality of aligned drill guidebores extending from the contoured articulation surface of the secondpatella trial portion, through the second patella trial portion andthrough the second base portion to the flat patella bone-facing surfaceof the second base portion. The alignment of the drill guide bores ofthe second base portion and second patella trial portion does not changeas the second base portion is rotated on the second bone-grippingcomponent and the positions of the aligned drill guide bores of thesecond end portion with respect to the resected patellar surface changesas the second base portion is rotated on the second bone-grippingcomponent.

In this embodiment, the second bone-gripping component may comprise apedestal and a plurality of spikes extending outwardly from thepedestal.

In this embodiment, a portion of each bore through the second patellatrial portion may have a larger diameter than the aligned portion ofsuch bore through the second base portion.

In this embodiment, the second base portion and the second patella trialportion may be integral or may comprise independent components connectedto define an assembly.

In this embodiment, the contoured articulation surface of the secondpatella trial portion may be asymmetric.

In this embodiment, the second end portion of the patella drill guidemay have a thickness extending from the contoured articulation surfaceof the second patella trial portion to an exposed surface of the secondbase portion, the second patella trial portion may have edges, includingopposite edges. The thickness of the second end portion of the patelladrill guide may vary from one edge of the second patella trial portionto the opposite edge and in at least one cross-sectional view, and themaximum thickness of the second end portion of the patella drill guidemay be at a position between the opposite edges of the second patellatrial portion at a distance from one edge of more than half the distancebetween the opposite edges.

In this embodiment, the first and second patella trial portions may beof different size, and the distance between opposite edges of the firstpatella trial portion may be different from the distance between theopposite edges of the second patella trial portion.

In another more particular embodiment, the patella drill guide furthercomprises a handle and a clamping mechanism connected to the handle. Inthis embodiment, the handle is connected to the base portion of thepatella drill guide. In this embodiment, the clamping mechanism maycomprise a cantilever spring member extending from the handle to an endspaced from and aligned with the base portion and a bone-gripping memberon the end of the cantilever spring member facing and spaced from thebone-gripping component on the base portion. In this embodiment, theclamping mechanism may further comprise a deflector connected to thehandle and operable to selectively deflect the bone-gripping member onthe cantilever spring member away from the bone-gripping component onthe base portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is a perspective view of one embodiment of a patella drill guideincorporating the principles of the present invention;

FIG. 2 is a top plan view of one end portion of the patella drill guideof FIG. 1;

FIG. 3 is an enlarged side view of one end portion of the patella drillguide of FIGS. 1-2, illustrating the end portion secured to a resectedpatella and with an example of a suitable countersink, depth-controllingdrill bit;

FIG. 4 is an enlarged side view of the patella drill guide of FIG. 3with the base and patella trial of the drill guide turned ninety degreesfrom the position shown in FIG. 3, shown secured to a resected patellabut without the countersink, depth-controlling drill bit;

FIG. 5 is a side elevation view of an alternative embodiment of thepatella drill guide, shown clamping a resected patella;

FIG. 6 is a side elevation view of the embodiment of the patella drillguide of FIG. 5, shown with the patella drill guide pivoted 90 degreeswith respect to the patella;

FIG. 7 is a side elevation view of an embodiment of a patella trialcomponent;

FIG. 8 is a side elevation view of an alternative base portion of apatella drill guide for use with the patella trial component of FIG. 7;

FIG. 9 is a top plan view of an alternative base portion of a patelladrill guide that may be used with the patella trial component of FIG. 7;

FIG. 10 is a side elevation of another alternative base portion of apatella drill guide for use with the patella trial component of FIG. 7;

FIG. 11 is a top plan view of the base portion of the patella drillguide of FIG. 10

FIG. 12 is a side elevation of another alternative base portion of apatella drill guide that may be used with the patella trial component ofFIG. 7; and

FIG. 13 is a top plan view of the base portion of FIG. 12.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,etcetera, may be used throughout the specification in reference to theorthopaedic implants and surgical instruments described herein as wellas in reference to the patient's natural anatomy. Such terms havewell-understood meanings in both the study of anatomy and the field oforthopaedics. Use of such anatomical reference terms in the writtendescription and claims is intended to be consistent with theirwell-understood meanings unless noted otherwise.

Referring to FIG. 1, a first embodiment of a patella drill guide 10 isillustrated. The illustrated patella drill guide 10 comprises a firstbone-gripping component 12, a second bone-gripping component 14, a firstbase portion 16, a second base portion 18, a first patella trial portion20, a second patella trial portion 22 and an arm 24 connecting the twobase portions 16, 18. In the first embodiment, the first and secondbone-gripping components 12, 14 are rotatably retained on the first andsecond base portions 16, 18.

Together, the first bone-gripping component 12, first base portion 16and first patella trial portion 20 comprise a first end portion of theillustrated patella drill guide 10, and the second bone-grippingcomponent 14, second base portion 18 and second patella trial portion 22comprise a second end portion. It should be understood that the firstand second end portions in the illustrated embodiment differ only insize. Only the details of first end portion are described below. Itshould be understood that the following detailed description of thefirst end portion applies to the second end portion as well unlessexpressly distinguished. In the drawings, parts of the second endportion that correspond with parts of the first end portion areidentified with the same reference number as that used for the first endportion, followed by the prime symbol “′”.

In the first illustrated embodiment, the first and second bone-grippingcomponents 12, 14 comprise a plurality of pointed conical spikes 26. Thespikes are sized and shaped to be pushed into the resected posteriorsurface of a patella, such as surface 28 of patella 30 in FIGS. 3-4.Although three conical spikes 26 are shown in the accompanying drawings,it should be understood that fewer or more spikes can be used; example,a single spike 26D could be used, as shown in the embodiment of FIGS.12-13.

As shown in phantom in FIG. 3, the spikes 26 of the first illustratedbone-gripping component 12 are fixed to a pedestal 32 and extendoutwardly from the pedestal 32. The pedestal 32 may have a generallycylindrical outer surface and include mounting features so that thefirst base portion 16 may be rotatably mounted on the pedestal 32 of thefirst bone-gripping component 12. The first base portion 16 may includea cylindrical recess 34 (see FIGS. 3-4) to receive the pedestal 32. Thepedestal 32 and first base portion 16 may include complementarystructures to secure the pedestal 32 and base portion 16 together whileallowing for relative rotation about the central longitudinal axis 33 ofthe pedestal 32; such complementary structures could include, forexample, a groove and a set of flexible projections to allow thepedestal 32 to be snap-fit into the recess 34 of the base portion 16while allowing for full rotation about axis 33.

Other options are available for rotatably connecting the pedestal 32 andthe base portion 16. For example, a screw and a roller bearing could beused. Alternatively, the pedestal could be shaped to have a largerdiameter than the portion carrying the spikes 26, and a cover with ahole having a diameter greater than the diameter of the portion carryingthe spikes 26 and less than the diameter of the portion of the pedestalretained within the recess in the base portion; thus, the pedestal 32can be secured to the base portion 16 while allowing full relativerotation between these components.

It may be desirable to provide for locking the pedestal 32 and baseportion 16 in a plurality of relative rotational positions. For example,the outer surface of the pedestal 32 could comprise a ratcheted surface,and a pawl could be mounted within the base portion 16 so that thepedestal and base releasable lock into a number of positions. Otherlocking mechanisms could be employed as well.

If a single spike is used, it may not be necessary for the base to berotatably mounted on the base. Instead, the base and spike could berotated about the spike on the patella. Such an embodiment isillustrated in FIGS. 12-13.

The base portion 16 includes a flat, planar patella bone-facing surface36. As shown in FIGS. 3-4, this surface 36 is designed to be pressedflat against the posterior resected surface 28 of a patella 30. Therecess 34 is open through the surface 36 so that the spikes 26 extendoutwardly beyond the patella bone-facing surface 36.

In the illustrated embodiment, the patella trial portion 20 has acontoured articulation surface 38 spaced above the flat, planar patellabone-facing surface 36 of the base portion 16. The contouredarticulation surface 38 may be an anatomic one, such as is disclosed inU.S. Pat. No. 6,074,425, which is incorporated by reference herein inits entirety. The contoured articulation surface may be shaped asdisclosed in U.S. Pat. No. 7,972,383 or U.S. Pat. Publ. No. 2009-0326661A1, which are incorporated by reference herein in their entireties. Thecontoured articulation surface may also comprise a sombrero-shaped orsemi-sombrero-shaped surface. In general, the articulation surface 38 iscontoured to be shaped like the shape of the corresponding size ofpatella implant component.

In the illustrated embodiment, the distance between the contouredarticulation surface 38 and the flat, planar patella bone-facing surface36 defines the overall thickness of the end portion 40 of the patelladrill guide 10, and generally corresponds with the thickness of thecorresponding patella implant component. As shown in FIG. 3, thethickness of the end portion 40 varies from one edge 42 of the endportion 40 to an opposite edge 44 of the end portion 40 when viewed in acoronal plane. The maximum thickness of the end portion 40 is at thepeak 46 of the articulation surface 38, shown as thickness “t” in FIGS.3 and 4. The peak 46 is off-center in the illustrated embodiment, beinglocated at a position between the opposite edges 42, 44 at a distancemore than one half the distance between the opposite edges 42, 44; thisoffset is shown in FIG. 3 as distance “d” from the central axis 33 ofthe pedestal 32, the central axis 33 being one-half the distance betweenthe edges 42, 44.

The base portion 16 and the patella trial portion 20 of the firstillustrated embodiment have a plurality of aligned drill guide bores 50,52, 54 extending from the articulation surface 38 of the patella trialportion 20, through the body of the patella trial portion 20 and throughthe base portion 16 to the flat patella bone-facing surface 36 of thebase portion 16. As shown in FIG. 4, each drill guide bore 50, 52, 54comprises two portions: the portion 56, 58, 60 through the patella trialportion 20 and the aligned portion 62, 64, 66 through the base portion16. The portions 56, 58, 60 through the patella trial portion 20 havelarger diameters than the portions 62, 64, 66 through the base portion16, and define annular shoulders, shown in FIGS. 3 and 4 at 61, 63 and65. The diameters of these portions 56, 58, 60, 62, 64, 66 correspondwith the diameters of a collar portion 68 and fluted portion 70 of thecountersink drill bit 72, shown in FIG. 3; the diameters of the portions62, 64, 66 through the base portion 16 correspond with the diameters ofthe mounting pegs on the patella implant component. In use, the annularshoulders 61, 63, 65 limit movement on the drill bit 72 into the patella30 by serving as a stop for the collar portion 68 of the drill bit 72;the thickness of the base portion 16 and the length of the flutedportion 70 of the drill bit thereby control the depth of the holesdrilled into the patella. This depth generally corresponds with thelengths of the mounting pegs on the patella implant component.

As can be seen in FIGS. 1 and 2, the aligned bores 50, 52, 54 in theillustrated embodiment are spaced in a triangular pattern on the endportion 40. The number of bores and spacing between the bores 50, 52, 54correspond with the number and spacing of the mounting pegs on thepatella implant component. It should be understood that the number andspacing of the bores may be adjusted from the illustrated embodiment,depending on the number and spacing of the mounting pegs on the patellaimplant component.

In the first illustrated embodiment, the base portion 16 and patellatrial portion 20 are discrete, independent components that are connectedto define an assembly. Although not illustrated, it should be understoodthat any suitable connection mechanism may be used to assemble thesecomponents 16, 20, such as complementary projections and recesses for asnap fit arrangement. It may be desirable to allow the surgeon to changethe patella trial portions 20 intraoperatively so that different sizesor shapes of articulation surfaces may be trialed on the same baseportion 16. It should also be understood that the base portion 16 andpatella trial portion 20 may instead comprise a single, integralcomponent.

Trialing of different sizes of patella implant components can beaccomplished with the illustrated embodiment. As indicated above, theillustrated patella drill guide 10 includes a second end portion 40′ atthe opposite end of the arm 24. The second end portion 40′ in theillustrated embodiment is substantially the same as the first endportion 40, differing only in size. The above description of the firstend portion 40 thus applies to the second end portion 40′ as well. Withthe illustrated embodiment, the surgeon may trial two different sizes ofcomponents before drilling the holes for the mounting pegs. Although theillustrated embodiment has two similar end portions 40, 40′, it shouldbe understood that a patella drill guide utilizing the principles of thepresent invention may include only a single end portion. In addition, asurgical kit may include multiple patella drill guides, either single ordouble-ended, to provide the surgeon with multiple sizes of patellatrial portions to use as trials.

In the embodiment illustrated in FIG. 1, the arm 24 connecting the twoend portions 40, 40′ may optionally include cutouts 41, 41′ definingwindows through which the surgeon may see the edge of the patella whenthe drill guide 10 is mounted on the patella.

The patella drill guide of the present invention may also include otherfeatures. For example, a clamping mechanism may be included for clampingthe patella drill guide against the posterior surface of the patella. Anexample of such a clamping mechanism is illustrated in the embodiment ofFIGS. 5-6. Many of the features of this embodiment are similar to thefeatures of the first embodiment described above; for such similarfeatures, the same reference numbers have been used in FIGS. 5-6,followed by the letter “A”. It should be assumed that the abovedescription applies as well to features bearing the same referencenumerals in FIGS. 5-6 as in FIGS. 1-4.

In the patella drill guide 10A of FIGS. 5-6, there is a single endportion 40A having features like those described above. Instead of beingconnected to a second end portion, the end portion 40A of FIGS. 5-6 isconnected to a handle 80. The handle 80 also houses one end of acantilever spring element 82 that extends from the handle 80 to a secondend aligned beneath the base portion 16A. The second end of thecantilever spring element 82 carries a bone-gripping member 84 that isaligned along the central axis 33 of the pedestal 32. The bone-grippingmember 84 can be deflected away from the base portion 16A by depressinga deflector 86 that operates against a portion of the cantilever springelement 82 between the two ends of the spring element 82. In use, thebone-gripping member 84 acts against the anterior surface 88 of thepatella 30 so that the patella is effectively held between thebone-gripping member 84 and the patella bone-facing surface 36A of thebase portion 16A. As can be seen from FIGS. 5-6, the clamp defined bythe bone-gripping member 84, spring element 82, handle 80 and endportion 40A allow for the spikes 26A of the end portion 40A to be setinto the resected patella surface and allow for full rotation of thebase portion 16A, patella trial portion 20A and bone-gripping member 84about the pedestal 32A so that the surgeon may have a firmer hold of thepatella as the trialing and drilling processes are performed.

It should be understood that the specific clamping mechanism describedabove and illustrated in FIGS. 5-6 is one example of a suitable clampingmechanism. Other clamping mechanisms may be used with the rotatabledrill guide and are within the scope of the invention unless expresslylimited to a particular clamping mechanism.

Other alternative embodiments are illustrated in FIGS. 7-9, FIGS. 10-11and FIGS. 12-13. Many of the features of these embodiments are similarto the features of the embodiments described above; for such similarfeatures, the same reference numbers have been used in FIGS. 7-9,followed by the letter “B”, in FIGS. 10-11, followed by the letter “C”and in FIGS. 12-13, followed by the letter “D”. It should be assumedthat the above description applies as well to features bearing the samereference numerals in FIGS. 7-13 as in FIGS. 1-6 unless specificdifferences are called out.

In these embodiments, the base portion 16B, 16C, 16D and the patellatrial portion 20B are discrete independent components that are assembledfor use. However, in these embodiments, the patella trial portion 20Bdoes not have any guide bores. Instead, the patella trial portion 20Bhas a plurality of pegs 100, 102, 104 that are sized and positioned tobe received within the drill guide bores 50B, 52B, 54B, 50C, 52C, 54C,50D, 52D, 54D that extend from the upper surface 106, 106C, 106D to thepatella bone-facing surface 36B, 36C, 36D of the base portion 16B, 16C,16D. The base portion 16B, 16C, 16D has an edge 108, 108C, 108D thatextends between the upper surface 106, 106C, 106D and the patellabone-facing surface 38B, 38C, 38D and around part of the circumferenceof the base portion 16B, 16C, 16D. For these embodiments, the patellatrial portion 20B has a reduced thickness, to account for the thicknessof the base portion 16B, 16C, 16D when trialing the assembly on thepatella.

FIGS. 9-13 illustrate some optional additional features that may be usedwith the base portion 16B, 16C, 16D of FIGS. 8-13. In these embodiments,the edge 108, 108C, 108D includes a plurality of spaced cut-outs orrecesses 110, 112, 114, 110C, 112C, 114C, 110D, 112D, 114D through whichthe resected posterior surface 28B, 28C, 28D of the patella 30B, 30C,30D may be viewed. The upper surface 106, 106C, 106D of the base portion16B, 16C, 16D includes sizing indicia 116, 116C, 116D so that thesurgeon can view the resected patella surface 28B, 28C, 28D juxtaposedwith the sizing indicia 116, 116C, 116D to determine the optimum size ofpatella implant component to be implanted. These embodiments areparticularly beneficial if multiple sizes of patella implant componentshave commonly sized and positioned mounting pegs, so that the same drillguide 10B, 10C, 10D can be used for multiple sizes of patella implantcomponents.

In the embodiment of FIGS. 8-9, the base portion 16B has a constantthickness between the upper surface 106 and the patella bone-facingsurface 36B; the thickness corresponds with the thickness of the pegs100, 102, 104 of the trial portion 20B. In the alternative embodimentsof FIGS. 10-13, the thickness of the base portion 16C, 16D varies: nearthe cut-outs or recesses 110C, 112C, 114C, 110D, 112D, 114D thethickness of the base portion 16C, 16D is less than the thickness nearthe drill guide bores 50C, 52C, 54C, 50D, 52D, 54D; for example, thethickness of the base portion 16C, 16D near the cut-outs or recesses110C, 112C, 114C, 110D, 112D, 114D may be about 2 mm, while thethickness of the base portion 16C, 16D near the drill guide bores 50C,52C, 54C, 50D, 52D, 54D may be about 6 mm. The varying thickness of thebase portion may be advantageous in that the relatively thin areasaround the cut-outs or recesses 110C, 112C, 114C, 110D, 112D, 114D, makethe size markings 116C, 116D more proximate to the patella bone surface28C, 28D and therefore more readable. In addition, the thicker centersection around the drill guide bores 50C, 52C, 54C, 50D, 52D, 54D may beuseful in reducing the number of drill bits included in the instrumentset. Typically, an instrument set would include a drill bit with a depthstop for drilling holes at the appropriate depth to receive pegs ofother components, such as the femoral implant component. The thickercenter section of the base portion 16C, 16D would allow this same drillbit, with the same depth stop, to be used to drill the holes for thepatella implant component at the appropriate depth for the patellaimplant component.

The embodiment of FIGS. 12-13 differs from that of FIGS. 10-11 in thatthe bone-gripping component 12D in the embodiment of FIGS. 12-13comprises a single spike 26D fixed to the base portion 16D. With thisembodiment, the entire assembly, including the base portion 16D, trialportion 20D and spike 26D, rotate as a unit about a longitudinal axisthrough the spike 26D when the spike is pressed into the resectedsurface 28D of the patella 30D. Such a fixed spike 26D could also beused in place of the plurality of spikes 26, 26A, 26B, 26C mounted on apedestal 32, 32A, 32B, 32C, as in the embodiments of FIGS. 1-11.

Although there are advantages to using the trialing and guide systemillustrated in FIGS. 7-13, it should be understood that variations maybe made. For example, the discrete patella trial portion 20B couldinclude guide bores that will align with the guide bores 50B, 52B, 54Bwhen the trial portion 20B and base portion 16B, 16C are assembled. Insuch an embodiment, a mounting mechanism other than the pegs 100, 102,104 would be employed. In addition, although advantageous, the baseportion 16B, 16C need not include the cut-outs/recesses 110, 112, 114 orsizing indicia 116.

All of the illustrated embodiments may be made of standard polymeric ormetallic materials used in the field of surgical instruments, and maycomprise assemblies of different such materials. Conventionalmanufacturing processes may be used. The invention is not limited to anyparticular material or manufacturing process unless expressly called forin the claims.

In use, the surgeon would first prepare the patella by resecting theposterior surface of the patella to create a flat, planar surface, suchas surface 28 of patella 30. For the embodiments of FIGS. 1-6, thesurgeon would then estimate the size of patella implant component thatwould be needed by the particular patient and select an appropriatelysized patella drill guide, such as drill guide 10, and then select theappropriately sized end portion, such as first end portion 40. Thesurgeon would then push the spikes 26 of the first bone-grippingcomponent 12 into the resected bone surface 28 until the patellabone-facing surface 36 of the base portion 16 is flat against theresected bone surface 28. With the end portion 40 thus fixed to thepatella 30, the patella may be positioned so that the articulationsurface 38 of the patella trial portion 20 engages an articulationsurface of the femoral trial component (not shown). The surgeon can thentake the patient's knee through a range of flexion and extension, andevaluate the interaction of the patellar trial articulation surface 38and the articulation surface of the femoral trial component. As thepatient's knee is taken through the range of motion, the surgeon mayadjust the orientation of the patella trial portion 20 by turning thebase portion 16, 16A, 16B, 16C and attached patella trial portion 20,20A, 20B on the pedestal 32, 32A, 32B, 32C until the surgeon issatisfied that the orientation of the articulation surface 38, 38A, 38Bis optimum. In the case of the embodiment of FIGS. 12-13, the baseportion 16D and attached patella trial portion 20D are turned about theaxis through the spike 26D until the surgeon is satisfied that theorientation of the articulation surface 38B is optimum. Since theorientation of the aligned bores 50, 52, 54, 50A, 52A, 54A, 50B, 52B,54B, 50C, 52C, 54C, 50D, 52D, 54D with respect to the patella changes asthe base portion 16, 16A, 16B, 16C, 16D and attached patella trialportion 20, 20A, 20B are turned, the bores 50, 52, 54, 50A, 52A, 54A,50B, 52B, 54B, 50C, 52C, 54C, 50D, 52D, 54D should then be in theoptimum orientation and position. The surgeon may then drill through theoptimally-located bores 50, 52, 54, 50A, 52A, 54A, 50B, 52B, 54B, 50C,52C, 54C, 50D, 52D, 54S to create mounting holes in the patella. Thedepth of each hole may be set if the drill bit has a collar and boresinclude shoulders, such as collars 68 and shoulders 63 shown in FIG. 3.The patella drill guide 10, 10A, 10B, 10C, 10D may then be removed fromthe prepared patella and the patella implant component may be implanted,with its mounting pegs received in the drilled holes and its orientationoptimized for proper tracking with respect to the femoral implantcomponent.

For the embodiments of FIGS. 7-13, a surgical kit using the features ofthis embodiment could include multiple sizes of patella trial portions20B corresponding with each size of implant component. The surgeon wouldmount the base portion 16B, 16C, 16D on the resected surface 28B, 28C,28D of the patella by pressing the spikes 26B, 26C or spike 26D into thepatella surface 28B, 28C, 28D and observing the patella edge through therecesses 110, 112, 114, 110C, 112C, 114C, 110D, 112D, 114D and comparingthe patella edge with the sizing indicia 116, 116C, 116D. The surgeonwould then select an appropriately sized trial portion 20B and assemblethe selected trial portion 20B on the base portion 16B, 16C, 16D byinserting the pegs 100, 102, 104 into the drill guide bores 50B, 52B,54B, 50C, 52C, 54C, 50D, 52D, 54D in the base portion 16B, 16C, 16D. Thesurgeon would then trial the assembly by moving the patient's kneethrough flexion and extension. During trialing, the surgeon may rotateor pivot the base portion 16B, 16C on the pedestal 32B, 32C (or the baseportion 16D about central longitudinal axis of spike 26D) until theorientation of the trial portion 20B is optimized. The trial portion 20Bmay then be removed from the base portion 16B, 16C, 16D and holesdrilled through the bores 50B, 52B, 54B, 50C, 52C, 54C, 50D, 52D, 54D inthe base portion. In these embodiments, the upper surface 106B, 106C,106D of the base portion 16B, 16C, 16D around the drill guide bores 50B,52B, 54B, 50C, 52C, 54C, 50D, 52D, 54D would serve to limit the depth ofthe drilled hole if a drill bit having a depth-setting collar is used.The patella drill guide 10B, 10C, 10D may then be removed from theprepared patella and the patella implant component may be implanted,with its mounting pegs received in the drilled holes and its orientationoptimized for proper tracking with respect to the femoral implantcomponent.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected. Other features maybe incorporated in the patella drilling system, such as the featuresdisclosed in the following U.S. Provisional patent applications filedconcurrently herewith: U.S. Provisional Patent Application Ser. No.61/540,049 entitled “Clamping Patella Drill Guide”, filed by RichardSpencer Jones, Martin W. Roche and Abraham P. Wright; and U.S.Provisional Patent Application Ser. No. 61/540,053 entitled “PatellaDrilling System”, filed by Raymond E. Randle, Martin W. Roche andAbraham P. Wright. The complete disclosures of these patent applicationsare incorporated by reference herein.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the method, apparatus, and system describedherein. It will be noted that alternative embodiments of the method,apparatus, and system of the present disclosure may not include all ofthe features described yet still benefit from at least some of theadvantages of such features. Those of ordinary skill in the art mayreadily devise their own implementations of the method, apparatus, andsystem that incorporate one or more of the features of the presentinvention and fall within the spirit and scope of the present disclosureas defined by the appended claims.

We claim:
 1. A combination of patella drill guide and trial for use inpreparing a resected patellar bone surface to receive a prostheticpatellar implant for a patient's knee joint, the combination of thepatella drill guide and trial comprising: a body having a flat patellabone-facing surface and a contoured articulation surface spaced aboveand opposite to the flat patella bone-facing surface; at least one spikeextending outwardly from the flat patella bone-facing surface in anopposite direction to and away from the contoured articulation surface;wherein the contoured articulation surface is linked to the flat patellabone-facing surface and has a curved shape configured for evaluating atrack of the patella during flexion of the knee joint; wherein: the bodyof the combination of the drill guide and trial has a plurality of drillguide bores extending through the flat patella bone-facing surface, thebody and the contoured articulation surface along parallel longitudinalaxes; each of the drill guide bores has a length extending from the flatpatella bone-facing surface to the contoured articulation surface; thelength of one of the drill guide bores is greater than the length ofanother one of the drill guide bores; the flat patella bone-facingsurface has a periphery; and the body has a varying thickness betweenthe flat patella bone-facing surface and the contoured articulationsurface, the thickness of the body being greatest at a position spacedfrom the periphery of the flat patella bone-facing surface, a lineintersecting the greatest thickness of the body and perpendicular to theflat patella bone-facing surface intersects the flat patella bone-facingsurface at a position spaced from the periphery of the flat patellabone-facing surface.
 2. The combination of the patella drill guide andtrial of claim 1, wherein the at least one spike comprises a pluralityof spikes.
 3. The combination of the patella drill guide and trial ofclaim 1, wherein each of the drill guide bores has a first largerdiameter portion aligned and connected with a second smaller diameterportion, the first larger diameter portion of each of the drill guidebores extending through the contoured articulation surface and thesecond smaller diameter portion extends from the first larger diameterportion to the flat bone-facing surface.
 4. The combination of thepatella drill guide and trial of claim 1, wherein the contouredarticulation surface has a shape that matches a shape of the prostheticpatellar implant.
 5. The combination of the patella drill guide andtrial of claim 1, wherein the contoured articulation surface isasymmetric.
 6. The combination of the patella drill guide and trial ofclaim 1, wherein the body comprises a base portion and a trial portion,wherein the base portion defines the flat patella bone-facing surfaceand the trial portion defines the contoured articulation surface.
 7. Thecombination of the patella drill guide and trial of claim 1, furthercomprising a rotatable member mounted in a recess in the flat patellabone-facing face, wherein the at least one spike extends outward fromthe rotatable member and a position of each of the drill guide boreswith respect to the resected patellar bone surface changes as the flatpatella bone-facing surface is rotated on the at least one spike.
 8. Thecombination of the patella drill guide and trial of claim 7, wherein theat least one spike comprises a plurality of spikes.
 9. The combinationof the patella drill guide and trial of claim 1, wherein the flatpatella bone-facing surface and the contoured articulation surface areintegral.
 10. The combination of the patella drill guide and trial ofclaim 1, further comprising a handle extending outward from the flatpatella bone-facing surface and a clamping mechanism connected to thehandle.
 11. The combination of the patella drill guide and trial ofclaim 1, wherein the plurality of the drill guide bores comprise threedrill guide bores spaced in a triangular pattern.
 12. The combination ofthe patella drill guide and trial of claim 11, wherein the at least onespike is positioned between the three drill guide bores.